linux-kernel - Re: [PATCH v4 07/15] mtd: nand: move Samsung specific init/detection logic in nand

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Message-ID: <cc948f6b-c9b1-5a15-544c-962c894b7c7d@gmail.com>
Date:   Wed, 11 Jan 2017 14:02:36 +0100
From:   Marek Vasut <marek.vasut@...il.com>
To:     Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc:     Richard Weinberger <richard@....at>, linux-mtd@...ts.infradead.org,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Cyrille Pitchen <cyrille.pitchen@...el.com>,
        Icenowy Zheng <icenowy@...c.xyz>, Valdis.Kletnieks@...edu,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 07/15] mtd: nand: move Samsung specific init/detection
 logic in nand_samsung.c

On 01/11/2017 08:57 AM, Boris Brezillon wrote:
> On Tue, 10 Jan 2017 20:00:28 +0100
> Marek Vasut <marek.vasut@...il.com> wrote:
> 
>> On 01/07/2017 08:49 AM, Boris Brezillon wrote:
>>> On Sat, 7 Jan 2017 00:53:24 +0100
>>> Marek Vasut <marek.vasut@...il.com> wrote:
>>>   
>>>> On 01/04/2017 06:08 PM, Boris Brezillon wrote:  
>>>>> On Wed, 4 Jan 2017 16:14:07 +0100
>>>>> Marek Vasut <marek.vasut@...il.com> wrote:
>>>>>     
>>>>>> On 01/03/2017 02:01 PM, Boris Brezillon wrote:    
>>>>>>> Move Samsung specific initialization and detection logic into
>>>>>>> nand_samsung.c. This is part of the "separate vendor specific code from
>>>>>>> core" cleanup process.
>>>>>>>
>>>>>>> Signed-off-by: Boris Brezillon <boris.brezillon@...e-electrons.com>      
>>>>>>
>>>>>> [...]
>>>>>>    
>>>>>>> diff --git a/drivers/mtd/nand/nand_ids.c b/drivers/mtd/nand/nand_ids.c
>>>>>>> index b3a332f37e14..05e9366696c9 100644
>>>>>>> --- a/drivers/mtd/nand/nand_ids.c
>>>>>>> +++ b/drivers/mtd/nand/nand_ids.c
>>>>>>> @@ -10,7 +10,7 @@
>>>>>>>  #include <linux/mtd/nand.h>
>>>>>>>  #include <linux/sizes.h>
>>>>>>>  
>>>>>>> -#define LP_OPTIONS NAND_SAMSUNG_LP_OPTIONS
>>>>>>> +#define LP_OPTIONS 0
>>>>>>>  #define LP_OPTIONS16 (LP_OPTIONS | NAND_BUSWIDTH_16)
>>>>>>>  
>>>>>>>  #define SP_OPTIONS NAND_NEED_READRDY
>>>>>>> @@ -169,10 +169,12 @@ struct nand_flash_dev nand_flash_ids[] = {
>>>>>>>  };
>>>>>>>  
>>>>>>>  /* Manufacturer IDs */
>>>>>>> +extern const struct nand_manufacturer_ops samsung_nand_manuf_ops;      
>>>>>>
>>>>>> Is the extern needed ?    
>>>>>
>>>>> Yes, unless you have another solution. If you remove the extern keyword
>>>>> you just redeclare samsung_nand_manuf_ops here, which is not what we
>>>>> want.    
>>>>
>>>> Maybe some accessor function can help ?
>>>>  
>>>
>>> You mean, in nand_ids.c
>>>
>>>     const struct nand_manufacturer_ops *get_samsung_nand_mafuf_ops();
>>>
>>>     struct nand_manufacturers nand_manuf_ids[] = {
>>>     ...
>>> 	{NAND_MFR_SAMSUNG, "Samsung", get_samsung_nand_mafuf_ops},
>>>     ...
>>>     };
>>>
>>> and then, in nand_samsung.c
>>>
>>>     const struct nand_manufacturer_ops *get_samsung_nand_mafuf_ops()
>>>     {
>>> 	return &samsung_nand_mafuf_ops;
>>>     }  
>>
>> Yeah, something like that.
>>
>>> What's the point of this extra indirection? I mean, in both cases you
>>> use a symbol that is not part of the same source file, so you'll have
>>> to define this symbol (using a function prototype or an extern object
>>> definition).
>>> Is this all about fixing checkpatch warnings, or do you have a problem
>>> with objects shared between different source files?  
>>
>> The later, separating this with an accessor function feels a bit cleaner
>> to me than using extern foo.
>>
>>> Now, I agree that the current approach is not ideal. A real improvement
>>> would be to let the NAND manufacturer drivers (nand_<vendor>.c) register
>>> themselves to the core. Something similar to CLK_OF_DECLARE() or
>>> IRQCHIP_DECLARE() for example. But that means creating a dedicated
>>> section for the nand_manufs_id table, and it's a lot more invasive than
>>> the current approach.  
>>
>> Well this would be awesome, but this can also be done later. I presume
>> you'll get to it eventually anyway, as soon as you'll be annoyed enough
>> with the current ugly-ish implementation.
>>
> 
> If we plan to rework it this way, I'd like to keep the existing
> approach (with the extern) to avoid changing the prototype of
> nand_manufacturer once again when we rework the nand_manufacturer
> registration logic.
> 
> Also note that in v6 I'm keeping a pointer to the nand_manfucturer
> object in nand_chip, so that if we ever need to print the manufacturer
> name we don't have to search again in the NAND manufacturer table.
> After this rework, I no longer store the manufacturer_ops directly in
> nand_chip, and have to access them by doing
> chip->manufacturer.desc->ops->xxx.
> 
> Which means, with your solution, I'll have to do
> 
> 	ops = nand_get_manufacturer_ops(chip->manufacturer.desc);
> 	ops->xxx();
> 
> instead of
> 
> 	chip->manufacturer.desc->ops->xxx();
> 

All right, I think we can live with this either way.

-- 
Best regards,
Marek Vasut